<!--使用css样式表定义方式以.xxx命名-->.btncss {
    background-color: red;
    font-size: 60px;
    color: yellow;
}

#header {
    background-color: black;
    color: white;
    text-align: center;
    padding: 0.25rem;
}

#nav {
    line-height: 30px;
    background-color: #C43030;
    height: 300px;
    width: 100px;
    float: left;
    padding: 5px;
}

#section {
    width: 350px;
    float: left;
    padding: 10px;
}

#footer {
    background-color: #C71F1F;
    color: white;
    clear: both;
    text-align: center;
    padding: 5px;
}

.isp {
    background: #C71F1f;
    width: 100px;
    height: 200px;
}

#pdiv {
    color: #C71F1F;
    font-size: 50;
}

h3 {
    color: red;
    text-align: left;
    font-size: 8pt;
}